Using the techniques of transmission electron microscopy (TEM), the epilayers of GaN (c-GaN) with zincblende structure grown on (001) GaAs substrate and of GaN (h-GaN) with wurtzite structure grown on (0001) sapphire were studied. We found that both c-GaN and h-GaN epilayers are single crystalline. For c-GaN grown on GaAs, the film/substrate orientation relationship was determined to be (001)GaN // (00l)GaAs, [220] GaN // [220]GaAs, [2[overline 2]0]GaN // [2[overline 2]0]GaAs. While for h-GaN grown on sapphire, it is (000l)GaN // (0001)Al₂O₃[11[overline 2]0]GaN//[1[overline 1]00] Al₂O₃ [1[overline 1]00]GaN//[11[overline 2]0] Al₂O₃....[ Read more ]

Using the techniques of transmission electron microscopy (TEM), the epilayers of GaN (c-GaN) with zincblende structure grown on (001) GaAs substrate and of GaN (h-GaN) with wurtzite structure grown on (0001) sapphire were studied. We found that both c-GaN and h-GaN epilayers are single crystalline. For c-GaN grown on GaAs, the film/substrate orientation relationship was determined to be (001)GaN // (00l)GaAs, [220] GaN // [220]GaAs, [2[overline 2]0]GaN // [2[overline 2]0]GaAs. While for h-GaN grown on sapphire, it is (000l)GaN // (0001)Al₂O₃[11[overline 2]0]GaN//[1[overline 1]00] Al₂O₃ [1[overline 1]00]GaN//[11[overline 2]0] Al₂O₃.

The lattice mismatches between the GaN and the two substrates were calculated, in the case of h-GaN/sapphire, the lattice mismatch is totally accommodated by the misfit dislocations at their interface. But in the case of c-GaN/GaAs, not all the lattice mismatch is accommodated by the misfit dislocations. The GaN lattice near the interface is distorted, so there is strain inside the c-GaN film. Besides, the average spacing of the misfit dislocations were determined to be ~18[Angstrom] for c-GaN/GaAs and ~17.3[Angstrom]for h-GaN/sapphire.

In both c-GaN/GaAs and h-GaN/sapphire, we observed that there are defects grown inside the GaN films. Inside the c-GaN film grown on GaAs, the main defect is stacking faults, the density of the stacking faults is found to be ~5 x10[to the power of 12]cm[to the power of negative -2]. While in h-GaN film grown on sapphire, the main defect is the dense threading dislocation. The density is ~3x10[to the power of 10]cm[to the power of -2].